Cross-field amplifier having a beam of electrons flowing through the interaction region orthogonally to microwave power flow

ABSTRACT

A cross-field microwave amplifier tube is disclosed. The crossed-field tube includes a cathode electrode structure concentrically disposed of a periodic slow wave circuit forming an anode to define a magnetron interaction region therebetween. A magnet is provided for producing an axially directed magnetic field in the magnetron interaction region. The slow wave circuit is severed to define an input port at one end and an output port at the other end for applying microwave signals to be amplified and for extracting the microwave signals. An electron gun is provided at one axial end of the magnetron interaction region for forming and projecting an annular stream of electrons into and through the magnetron interaction region to a collector electrode structure disposed at the opposite axial end of the magnetron interaction region. In this manner, the electrons are caused to drift through the interaction region with a substantial component of velocity orthogonal to the direction of signal power flow on the slow wave circuit, whereby electron noise on the electron stream is not strongly coupled to the slow wave circuit. By causing the electrons to drift through the interaction region to the collector structure the dynamic range of the crossed field amplifier is extended well into the small signal regime.

United States Patent [1 1 Farney [111 3,868,539 [451 'Feb. 25, 1975 [75] Inventor: George K. Farney, New Providence,

[73] Assignee: Varian Associates, Palo Alto, Calif.

[22] Filed: June 28, 1966 [21] Appl. No.: 561,220

[52] US. Cl. 315/393, 315/39.51 [51] Int. Cl. i. HOlj 25/34 [58] Field of Search 315/393, 39.51, 39.55,

[56] References Cited UNITED STATES PATENTS 3,448,330 6/1969 Farney 315/393 Primary ExaminerMaynard R. Wilbur Assistant ExaminerN. Moskowitz Attorney, Agent, or Firm-Stanley Z. Cole; David R.

Pressman [5 7] ABSTRACT A cross-field microwave amplifier tube is disclosed. The crossed-field tube includes a cathode electrode structure concentrically disposed of a periodic slow wave circuit forming an anode to define a magnetron interaction region therebetween. A magnet is provided for producing an axially directed magnetic field in the magnetron interaction region. The slow wave circuit is severed to define an input port at one end and an output port at the other end for applying microwave signals to be amplified and for extracting the microwave signals. An electron gun is provided at one axial end of the magnetron interaction region for forming and projecting an annular stream of electrons into and through the magnetron interaction region to a collector electrode structure disposed at the opposite axial end of the magnetron interaction region. In this manner, the electrons are caused to drift through the interaction region with a substantial component of velocity orthogonal to the direction of signal power flow on the slow wave circuit, whereby electron noise on the electron stream is not strongly coupled to the slow wave circuit. By causing the electrons to drift through the interaction region to the collector structure the dynamic range of the crossed field amplifier is extended well into the small signal regime.

8 Claims, 9 Drawing Figures "lIIIlIIIIIlll,.--- m B IO j' IS INJECTOR & POWER SUPPLY CROSSEO FIELD ANODE SUPPLY DEPRESSED COLLECTOR SUPPLY "'IIIIIIIIIIIIIa- INJECTOR POWER SUPPLY CROSSED FIG. 4 Km" "Hr 8 INVENTOR. 3 fl GEORG FARNEY I BY 1 TORNEY PATENTEDFEBZS ms 24 FIG.9 ,y

MICROWAVE POWER OUTPUT FIG. 8 I OPERATING RANGE OF PRIOR ART EMITTING SOLE, REENTRANT STREAM CROSSED FIELD AMPLIFIERS XINCREASE 0F OPERATING RANGE OBTAINED BY PRIOR ART INJECTED BEAM CROSSED FIELD AMPLIFIERS WITH INJECTION PARALLEL TO POWER FLOW ON THE CIRCUIT INCREASE OF OPERATING RANGE OBTAINED BY INJECTING THE BEAM THROUGH THE CIRCUIT IN A DIRECTION ORTHOGONAL TO THE DIRECTION INVENTOR.

0F MICROWAVE POWER FLOW ON THE CIRCUIT. BY

MICROWAVE POWER INPUT GE GE FARNEY TORNFY CROSS-FIELD AMPLIFIER HAVING A BEAM F ELECTRONS FLOWING THROUGH THE INTERACTION REGION ORTHOGONALLY TO MICROWAVE POWER FLOW The present invention relates in general to crossedfield microwave amplifier tubes and, more particularly, to an improved wide band crossed-field amplifier wherein the electron beam is injected into and caused to flow through the electronic interaction region in a direction orthogonal to the direction of microwave power flow on the slow wave circuit, whereby noise power on the electron stream is minimal and that noise power which is present in the beam is substantially decoupled from the microwave circuit. Such a tube configuration substantially extends the dynamic range of the amplifier down to the zero or near zero input signal regime, whereby the tubes are especially useful for, but not limited to use as, efficient low input signal amplifiers as required for use in electronic radar countermeasures.

Heretofore, microwave amplifier tubes have been proposed wherein a stream of electrons was to be injected into a reentrant stream crossed field interaction region from both ends thereof. In such a tube geometry the electron stream would flow into the interaction region in orthogonal relation to the direction of microwave power flow in the microwave circuit. Such a tube is proposed in an article entitled, Considerations Concerning The Construction Of An Injected Re-entrant Beam Forward Wave Crossed Field Amplifier, appearing in the Proceedings of the 5th International Congress on Microwave Tubes, Paris, Sept. 14-18 1964 at pages 300-304. However, in this proposed tube no separate collector electrode, separate from the anode circuit, was provided such that the space charge, in the absence of a strong signal on the microwave circuit, was allowed to build up in the interaction region. The problem with such a build up of the space charge is that the electrons due to their mutual repulsion build up into regions having relatively large turbulent gyrations about the magnetic field lines. These gyrations of the electrons constitute sources of substantial noise power that will couple to the microwave circuit and be amplified by the circuit by a mechanism known as the diocotron gain mechanism. This noise power, which is coupled to the slow wave circuit, produces substantial noise power in the low input signal regime, thereby preventing the tube from having a dynamic range which will extend into the zero or near zero input signal regime. The tube is operable in the large signal regime since a large input signal produces a phase locking mechanism which locks the phase of the spokes of space charge to the wave on the circuit, thus, discriminating against or locking out the noise power.

In the present invention, the electron stream is injected into the crossed-field interaction region as proposed previously. However, a collector electrode separate from the anode circuit is provided which causes the electrons to flow through and out of the interaction region. 'In this manner, space charge density is prevented from building up in the interaction region to a value sufficient to produce a substantial source of noise power which could be coupled to the microwave circuit. As a consequence the dynamic range of the amplifier is extended well into the low input signal regime. In a preferred embodiment, the electrons are caused to flow through the interaction region so quickly that essentially no noise power is coupled to the microwave circuit, whereby in the absence of an input signal to be amplified there is no output signal. In such an improved amplifier the electrons are drawn toward the anode microwave circuit and across the electric equipotential lines in direct proportion to the strength of the input signal on the microwave circuit, thereby converting a fraction of the available potential energy to microwave energy in proportion to the input signal strength. Multiple collector electrodes, operating at various intermediate potentials below anode potential are then preferably employed for collecting the various unconverted potential energies of the electron stream, whereby the efficiency of the tube is enhanced in the low signal regime.

The principal object of the present invention is the provision of an improved crossed-field microwave amplifier tube.

One feature of the present invention is the provision, in a microwave amplifier tube of the orthogonally injected reentrant stream type, of a collector electrode for causing the stream to pass through the interaction region to the collector in a transit time sufficiently short so as to prevent substantial generation of and coupling of noise power from the stream to the slow wave circuit, whereby the dynamic range of the amplifier is extended well into the low input signal regime.

Another feature of the present invention is the same as the preceding wherein the injected electron stream is caused to drift across the microwave circuit to a collector structure operating at one or more potentials negative with respect to the anode for reducing the standby power consumption of the tube.

Another feature of the present invention is the same as any one or more of the preceding features wherein the electrons are injected from a magnetically confined flow electron gun, whereby electron noise on the electron stream which can be coupled to the slow wave circuit is reduced to improve zero amaplitude input signal stability of the tube.

Another feature of the present invention is the provision of a magnetron injection type electron gun for injecting the electrons into the interaction region, whereby a large area cathode emitter is obtained.

Other features and advantages of the present invention will become apparent upon a perusal of the following specification taken in connection with the accompanying drawings wherein:

FIG. 1 is a transverse schematic line diagram of a microwave amplifier tube employing features of the present invention,

FIG. 2 is a sectional view of the structure of FIG. 1 taken along line 2-2 in the direction of the arrows and showing the power supplies,

FIGS. 3, 4 and 5 are views similar to that of FIGS. 1 and 2 showing alternative embodiments of the present invention,

FIG. 6 is a longitudinal sectional view of a linear crossed-field tube incorporating features of the present invention,

FIG. 7 is a plan view of the structure of FIG. 6 taken along line 7--7 in the direction of the arrows,

FIG. 8 is a plot of microwave power output versus microwave power input showing the gain characteristics of the prior art compared with those of the tube of the present invention, and

FIG. 9 is a schematic line diagram of a crossed-field amplifier employing an alternative collector structure of the present invention.

Referring now to FIGS. 1 and 2 there is shown a circular version of the crossed-field amplifier tube 1 of the present invention. A cylindrical non-emissive cathode sole electrode 2 as of copper, which is grooved to inhibit secondary emission, is surrounded by an anode electrode structure 3. The anode electrode 3 includes a microwave slow wave circuit 4 having an input terminal 5 for applying signals to be amplified and an output terminal 6 for extracting amplified signals. The anode electrode 3 includes a circuit sever potion 7 disposed between the input and output terminals of the slow wave circuit to prevent wave energy from circulating around the tube from output to input. A vacuum envelope 8 encloses the tube elements and is evacuated to a low pressure as of Torr.

A magnet 10 provides a magnetic field B which is applied axially of the cylindrical cathode in a crossed electric and magnetic field interaction region 9 defined by the annular region between the cathode 2 and anode 3. An annular thermionic electron emitter 11 is disposed at one end of the interaction region 9 for supplying electrons when heated to emitting temperature by conventional heater means, not shown.

An annular accelerator electrode 12 caps one end of the cathode sole 2 and includes an annular gap 13 in axial alignment with the interaction region 9 and through which electrons are injected into the interaction region 9 from the thermionic emitter 11. The applied magnetic field B extends into the region of the thermionic emitter 11 with the field lines B threading through the emitter l1, gap 13 and interaction region 9 to provide an immersed flow type of electron injection.

A primary collector electrode 14, as of copper, caps the other end of the cathode sole 2 and is held to the sole 2 via an insulator disk 15 as of alumina ceramic. A second annular collector electrode 16 as of copper extends radially out beyond the periphery of the first collector 14 for collecting electrons at a potential more nearly that of the anode potential.

An injector power supply 17 supplies an operating potential between the thermionic emitter 11 and the accelerator electrode 12. The sole 2 operates at the same potential as the accelerator electrode 12. A crossed-field anode supply 18 supplies operating voltage and current between the anode 3 and the sole 2.

A depressed collector supply 19 supplies a potential to the depressed collector 14 which is intermediate the thermionic emitter potential and the accelerating electrode potential. Alternatively, the depressed collector may be operated at cathode sole potential or at a potential below sole potential and only slightly more positive than emitter potential for reducing standby power consumption.

In operation, electrons are axially injected into the crossed-field interaction region 9. In the absence of an applied microwave signal on the slow wave circuit to be amplified, the magnetic field B confines the injected electrons to a hollow beam path 21 which remains at a relatively constant radius. The crossed electric and magnetic fields in the interaction region cause the electrons to have a spiralling trajectory around the cathode sole 2 at the radius of path 21. The spiralling hollow electron stream drifts through the crossed-field interaction region and is collected on the primary electron collector electrode 14, preferably operating just above the potential of the thermionic cathode emitter 11, whereby depressed collector operation is obtained to reduce standby power consumption of the tube 1.

In case an input signal to be amplified is present on the slow wave anode circuit 4, the electric fields of the signal wave extend into the primary electron stream 21 to interact with the circumferential velocity component of the spiralling electrons in the same manner as encountered in conventional crossed-field amplifier tubes. As a result some of the electron current is diverted from the stable spiralling path 21 and brought into closer proximity to the anode 3 for converting a fraction of the dc. power to microwave power on the circuit 4.

This diverted portion of the electron current interacts in the conventional crossed-field interaction manner with the rf fields on the slow wave circuit. The energy which is converted into microwave power is obtained from the dc power supply 18 connected between the sole electrode 2 and the anode 3. The electrons move radially from the stable hollow beam 21 toward the anode 3 traversing equipotential lines in the interaction space 9 and convert the dc power supply energy to microwave rf energy which is added to the slow wave circuit. The distance through which the electrons move toward the anode 3 is determined by the radial velocity since the axial velocity (and therefore the transit time through the interaction region 9) is fixed. The radial velocity is determined locally by the circumferential component of E and the axial magnetic field B; that is, v E (circumferential) /B The rf field intensity is, of course, a function of radial position and the rf field level on the slow wave circuit 4. As a result, the trajectories of the electrons in the interaction region are quite complex. In some cases, the rf field levels on the slow wave circuit 4 are sufficiently small that the electrons can traverse only part of the distance between the sole 2 and the anode 3 while traveling axially through the interaction space 9. In that event only a fraction of the total available potential energy is converted into microwave power. The electrons then continue to travel axially leaving the crossed-field interaction region 9 and are eventually collected upon the walls 8 of the tube 1 or upon the secondary collector electrode 16. In traveling to the secondary collector 16, the electrons experience an acceleration over a potential difference equal to that between full anode potential and the potential line upon which they were traveling as they left the crossed-field interaction region 9. This energy appears as heat to be dissipated upon the secondary collector electrode 16. The more energy which is converted directly to rf energy on the slow wave circuit leads to less energy which must be dissipated in the form of heat on the secondary collector electrode 16.

At very weak rf signals on the slow wave circuit, only a small amount of current is diverted from the spiralling, hollow beam path 21. In addition, only a fraction of this current reaches the slow wave anode circuit 4 with the rest being collected. upon the secondary electrode 16. This rf control of the magnitude of the current at low signal levels plus the possibility of this current traversing only part of the total distance between sole 2 and slow wave circuit 4 results in fractional potential energy conversion and yields a very large dynamic range capability for this tube configuration. Further, the ability to have a continuous variation in rf diversion of current from the primary to the secondary collector electrode tends to improve the efficiency of the conversion process at very low rf signal levels. That is, only an rf controlled fraction of the beam current will participate in the crossed-field interaction.

The gain from the amplifier can be made quite large by choosing a sufficiently long slow wave circuit. The circuit length and other dimensions are chosen so that the spiralling electron stream 21 makes less than one complete revolution around the sole electrode 2 during the transit time through the interaction region 9. This feature together with the presence of the drift space between the rf input 5 and output 6 on the slow wave circuit 4 provided by the sever 7 tends to inhibit the possible build up of coherent oscillations at frequencies corresponding to a slow wave circuit mismatch. This amplifier configuration is stable so far as noise is concerned because only the circumferential component of the noise is coupled to the circuit and whatever noise is contained in the rotating electron spiral is coupled to the slow wave circuit over only a fraction of its total length during the axial transit of the electrons through the interaction region. Note that the axial variations in velocity of the electrons which constitutes electron stream noise is not coupled to the slow wave circuit 4 because the direction of power flow on the slow wave circuit is orthogonal to the electric field of the noise power. Moreover the relatively short transit time of the electrons through the interaction region 9 prevents build up of space charge density in the interaction region 9. A buildup of space charge density in this region will lead to generation of noise power due to the space charge mutual repulsion which causes increased cyclotron orbits and turbulence of the electron flow. This turbulent electron flow constitutes noise power that has a substantial component with velocities parallel to the direction of power flow on the circuit and thus could couple to the circuit 4.

As a result the dynamic range of the amplifier tube 1 is extended well into the low signal regime and even down to zero signal amplitude as shown by reference to FIG. 8 wherein the dotted portion of the curve illustrates the extension of the dynamic range of the amplifier over the prior art.

Referring now to FIG. 3 there is shown an alternative embodiment of the present invention. The structure is essentially identical to that described previously with regard to FIGS. 1 and 2 with the exception that the electrons are injected into the crossed-field interaction region 9 from a magnetron injection type electron gun 22. More specifically the gun 22 includes a cylindrical thermionic emitter 23. A converging accelerating electrode 24 is radially spaced from the emitter 23 for providing an axially increasing radial accelerating field E at right angles to the axial magnetic field B which threads through the region between emitter 23 and anode 24. Under these conditions electrons are drawn from the emitter region and injected into the crossedfield interaction region 9.

This tube configuration has the advantage that it can use an emitting surface which is greater in area than that for the electron gun shown in FIGS. 1 and 2. Crossed-field injection guns are usually more noisy than are immersed flow electron guns.

However, in a tube of the present invention the axial noise components of the beam are not coupled to the orthogonally directed slow wave circuit and as a consequence the higher noise levels of the magnetron injection gun do not interfere with proper operation of the tube 1.

Referring now to FIG. 4 there is shown an alternative embodiment of the present invention. In this embodiment two tube structures similar to that shown in FIGS. 1 and 2 are axially mounted back to back such that the electron guns inject their electron streams into the tube from both ends toward the center collector 14. This permits a larger anode circuit 4 and twice the electron current. The secondary collector structures 16 are moved to opposite ends of the combined crossed-field interaction region 9. The result is a tube of the type having increased dynamic range and increase power output capacity.

Referring now to FIG. 5 there is shown an alternative embodiment of the present invention. In this embodiment the slow wave circuit is severed into two portions by a second sever 26. The ends of the circuit portions which have been severed are terminattd in matched resistive terminations 27 to prevent reflection of wave energy from the severed ends. The provision of the second circuit sever 26 and the matched terminations 27 permits the gain of the tube to be increased as compared to non severed circuit tubes because the tube is not transparent to wave reflections from the load. The second circuit sever 26 is preferably only as long in the circumferential direction, as one period of the periodic slow wave circuit 4 in order to prevent substantial debunching of the spiralling electron stream during the stream transit time across the second circuit sever 26.

Referring now to FIGS. 6 and 7 there is shown a linearized version of the circular crossed-field tube 1 of FIGS. 1 and 2. More particularly, the tube is equivalent to the circular geometry of FIGS. 1 and 2 which has been cut lengthwise and flattened out. The emitter 11 is a filamentary emitter extending along one side of the tube 1'. The accelerating electrode 12' is a plate having an elongated stream injection slot 13 extending parallel to the emitter 11'. The cathode sole electrode 2 is a plate extending lengthwise of the tube. The periodic anode circuit 4 overlays the sole plate 2 in spaced relation to define the crossed-field interaction region 9' therebetween. The primary and secondary collector electrodes 14' and 16, respectively, extend lengthwise of the tube 1' together with insulator 15' on the opposite side from the emitter 11'.

Signal wave energy to be amplified is applied to an input terminal 5' of the slow wave circuit 4. Amplified signal energy is extracted from the circuit 4 via output terminal 6 at the other end of the tube. The electron trajectories for the standby or zero amplitude input signal condition are as shown by the flow lines 32.

The performance of the tube 1 of FIGS. 6 and 7 is substantially the same as that of the tube of FIGS. 1 and 2 and as shown in FIG. 8 by the extended dynamic range portion. However, the efficiency of this tube 1' is inferior to that of the circular geometries because the electron stream is non-reentrant.

Referring now to FIG. 9 there is shown a crossedfield aamplifier tube 1 of the present invention which employs multiple collector electrodes operating at various intermediate potentials between those applied between the anode 4 and sole 2. More specifically the tube 1 is essentially identical to the structure of FIGS. 1, 2 and 3 except that additional collector electrodes 41, 42 and 43 are provided. The collector electrodes 4l-43 are insulated from each other via insulators 44, 45, 46 and 47. A power supply 48 having a plurality of outputs supplies separate operating ppotentials to the various additional collectors 41-43 which potentials are intermediate the potential of the anode 4 and sole 2.

The additional collectors serve to collect the electrons that have only partially interacted with the wave on the slow wave circuit. Such electrons have a substantial axial velocity and are on various equipotential lines intermediate the beam path 21 and the anode 4. The additional collectorss 41-43 are biased at these various intermediate potentials for collecting the electrons at less than anode potential such that the electrons are collected without further increasing their kinetic energy. In fact the electrodes could be biased at less than the various equipotentials on which the electrons leave the interaction region to collect. the electrons at lower kinetic energy and thus further improve the efficiency of the tube. The multistage collector of PK]. 9 allows a marked improvement in overall efficiency of the amplifier with particular improvement at low r.f. input signal levels. At large signal levels, close to the saturation point, all of the current participating in the interaction would be collected upon the anode slow wave circuit and, therefore, the high level efficiencies typical of crossed-field devices would be obtained.

The various intermediate potentials applied to the collector are derived from the secondary winding 50 of a transformer 51 the primary winding 52 of which is energized from the 60 Hz power line 53. The secondary winding 50 is tapped at various points and the ac output rectified by rectifiers 54 and the various rectified output voltages filtered by filter capacitors 55.

In the tubes of the present invention, any one of a number of conventional forward wave slow wave circuits 4 may be employed. Suitable forward wave circuits include, but are not limited to, the helix, reactively loaded interdigital line, and C strapped bar circuit.

In addition, the tubes may advantageously be employed as dual mode tubes in that the power output can be increased for pulsed operation relative to continuous wave output performance. This is accomplished by increasing the potential applied to the injector accelerating electrode 12 as compared to those potentials applied for C.W. operation.

Since many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

l. A crossed-field microwave amplifier tube including, means forming a cathode electrode, means forming an anode electrode structure operated in use at a potential positive with respect to said cathode and including a portion spaced from said cathode electrode to define an electronic interaction region therebetween, means for applying a magnetic field to the interaction region with the applied magnetic field being directed transversely to the electric field between said anode and cathode electrodes to form a crossed-field interaction region, said anode electrode structure including a periodic slow wave circuit portion disposed adjacent said crossed-field interaction region and having an input and output terminal said circuit being directed orthogonally to both the electric field and the magnetic field in the crossed-field interaction region such that signal wave power flow on said slow wave circuit is orthogonal to the crossed electric and magnetic fields, means for injecting a stream of electrons along the direction of the applied magnetic field with a substantial component of velocity orthogonal to the diection of signal power flow on said slow wave circuit, whereby electron noise on the electron stream is not strongly coupled to said slow wave circuit, and said anode structure means including a collector electrode portion disposed at at least one in the direction of said magnetic field end of a portion of said interaction region for causing the electron stream to flow through the interaction region to said collector electrode, thereby extending the dynamic range of the crossed-field ammplifier well into the low signal regime.

2. The apparatus of claim 1 wherein a portion of said collector electrode structure is electrically insulated from said anode slow wave circuit means and said cathode electrode structure and adapted to be operated at a potential intermediate the potentials applied to said anode circuit and cathode and disposed at the terminal end of the injected electron stream for collecting and dissipating the energy of at least a portion of the electron stream. whereby said collector is operable at a potential depressed with respect to said anode slow wave circuit for reducing the standby power consumption of the tube.

3. The apparatus of claim 1 wherein said means for injecting the electron stream includes, a thermionic emitter provideing a source of electrons, and wherein the applied magnetic field threads through said thermionic emitter for confining the flow of electrons from said emitter to a path with a substantial component parallel to the direction of the applied magnetic field between said anode and cathode electrode structures, whereby electron noise on the injected electron stream is not strongly coupled to said orthogonally directed slow wave circuit.

4. The apparatus of claim 1 wherein said means for injecting the electron stream includes, a thermionic emitter providing a source of electrons and having an emitting surface portion, and means forming an accelerating electrode structure spaced from said emitter for producing an electric field between said emitter and accelerator for drawing electrons therefrom into an electron stream, and wherein said means for applying the magnetic field applies the magnetic field to the region between said electron emitting surface and said accelerating electrode at a substantial angle to the electric field therebetween to form a crossed-field magnetron injection gun assembly.

5. The apparatus of claim 1 wherein said electron stream injecting means injects a pair of axially directed electron streams into the interaction region from opposite directions, whereby the available injected current is increased.

6. The apparatus of claim 1 wherein said slow wave circuit is a fundamental forward wave circuit.

interaction region is arcuate, said slow wave circuit is directed circumferentially of the arcuate electronic interaction region, and wherein the region of space between said anode and cathode electrodes is reentrant such that electrons may circulate about said anode circuit from said output terminal to said input terminal,

whereby the efficiency of the tube is increased. 

1. A crossed-field microwave amplifier tube including, means forming a cathode electrode, means forming an anode electrode structure operated in use at a potential positive with respect to said cathode and including a portion spaced from said cathode electrode to define an electronic interaction region therebetween, means for applying a magnetic field to the interaction region with the applied magnetic field being directed transversely to the electric field between said anode and cathode electrodes to form a crossed-field interaction region, said anode electrode structure including a periodic slow wave circuit portion disposed adjacent said crossed-field interaction region and having an input and output terminal said circuit being directed orthogonally to both the electric field and the magnetic field in the crossed-field interaction region such that signal wave power flow on said slow wave circuit is orthogonal to the crossed electric and magnetic fields, means for injecting a stream of electrons along the direction of the applied magnetic field with a substantial component of velocity orthogonal to the diection of signal power flow on said slow wave circuit, whereby electron noise on the electron stream is not strongly coupled to said slow wave circuit, and said anode structure means including a collector electrode portion disposed at at least one in the direction of said magnetic field end of a portion of said interaction region for causing the electron stream to flow through the interaction region to said collector electrode, thereby extending the dynamic range of the crossed-field ammplifier well into the low signal regime.
 2. The apparatus of claim 1 wherein a portion of said collector electrode structure is electrically insulated from said anode slow wave circuit means and said cathode electrode structure and adapted to be operated at a potential intermediate the potentials applied to said anode circuit and cathode and disposed at the terminal end of the injected electron stream for collecting and dissipating the energy of at least a portion of the electron stream, whereby said collector is operable at a potential depressed with respect to said anode slow wave circuit for reducing the standby power consumption of the tube.
 3. The apparatus of claim 1 wherein said means for injecting the electron stream includes, a thermionic emitter provideing a source of electrons, and wherein the applied magnetic field threads through said thermionic emitter for confining the flow of electrons from said emitter to a path with a substantial component parallel to the direction of the applied magnetic field between said anode and cathode electrode structures, whereby electron noise on the injected electron stream is not strongly coupled to said orthogonally directed slow wave circuit.
 4. The apparatus of claim 1 wherein said means for injecting the electron stream includes, a thermionic emitter providing a source of electrons and having an emitting surface portion, and means forming an accelerating electrode structure spaced from said emitter for producing an electric field between said emitter and accelerator for drawing electrons therefrom into an electron stream, and wherein said means for applying the magnetic field applies the magnetic field to the region between said electron emitting surface and said accelerating electrode at a substantial angle to the electric field therebetween to form a crossed-field magnetron injection gun assembly.
 5. The apparatus of claim 1 wherein said electron stream injecting means injects a pair of axially directed electron streams into the interaction region from opposite directions, whereby the available injected current is increased.
 6. The apparatus of claim 1 wherein said slow wave circuit is a fundamental forward wave circuit.
 7. The apparatus of claim 1 wherein said slow wave circuit includes a circuit sever intermediate said input and output terminals to separate the anode circuit into a pair of slow wave circuit portions and including a pair of resistive terminations provided at the severed ends of said circuit portions, whereby the gain of the tube is increased without producing regenerative oscillation in the tube.
 8. The apparatus of claim 1 wherein the electronic interaction region is arcuate, said slow wave circuit is directed circumferentially of the arcuate electronic interaction region, and wherein the region of space between said anode and cathode electrodes is reentrant such that electrons may circulate about said anode circuit from said output terminal to said input terminal, whereby the efficiency of the tube is increased. 